[Danielobito009]

Description

Implements language switcher persistence to LocalStorage, allowing users' selected language preferences to survive across sessions and page reloads.

Closes #455

Changes

• frontend/lib/storage.ts — New SSR-safe LocalStorage utility module

  • saveLocale() — Persists selected language to LocalStorage under airflex_locale key
  • loadLocale() — Retrieves saved language preference
  • clearLocale() — Clears stored preference
  • Gracefully handles SSR, private browsing mode, and quota exceeded errors

• frontend/hooks/useLocaleStorage.ts — New reusable locale management hook

  • getSavedLocale() — Returns saved locale or defaults to en if invalid/missing
  • persistLocale() — Validates and saves a locale
  • resetLocalePreference() — Clears stored locale preference

• frontend/components/LocaleInitializer.tsx — New client component for app-load initialization

  • Runs on mount to restore user's saved language preference
  • Redirects to saved locale if it differs from current
  • Transparent component (renders nothing)

• frontend/components/LanguageSwitcher.tsx — Updated to persist language selection

  • Calls saveLocale() when user selects a new language

• frontend/app/layout.tsx — Updated to initialize locale on app load

  • Added LocaleInitializer component to root layout

Acceptance Criteria

• ✅ Selecting a language saves it to LocalStorage under airflex_locale key
• ✅ On app load, saved language is applied before first paint
• ✅ Invalid or unsupported stored values are ignored, falling back to default locale
• ✅ Persistence helper is reusable and handles SSR/LocalStorage-availability safely
• ✅ Clearing LocalStorage reverts to default locale behavior

Testing

• Language selection persists across page reloads
• Invalid stored values don't break the app
• Private browsing mode and quota exceeded errors are handled gracefully
• Locale preference survives browser sessions